1. Technical Field
This invention relates to jet looms, and more particularly a device for controlling a plurality of weft yarn storing units for a jet loom which are adapted to selectively store a plurality of weft yarns.
2. Description of the Prior Art
A weft yarn storing unit for selecting and jetting free weft yarns, which comprises a motor and a storing mechanism as shown in FIG. 2, is well known in the art. The construction and operation of the unit will be described.
Before being jetted, a weft yarn from a package 1 is passed through a hollow shaft 2 rotated by a motor (not shown) and an arm 4 rotated together with the shaft 2, and wound on a drum 5 which is fixed by a magnet 9. At the weft yarn jetting timing, a solenoid is operated to disengage a pin 6 from the drum 5, and the weft yarn is unwound and inserted into the warp shed by the pneumatic force of a main nozzle. A sensor 7 for detecting the unwinding of a weft yarn is disposed beside the pin 6. When the number of times of unwinding corresponding to a woven fabric width is counted, the solenoid is deenergized and the pin 6 is inserted into a hole formed in the drum 5. As the weft yarn is jetted, the quantity of weft yarn wound on the drum is decreased. The remaining quantity of weft yarn on the drum is detected by an optical sensor 8, so that the motor coupled to the shaft 2 is started to supply the weft yarn.
A plurality of weft yarn storing units which are constructed as described above are set. The units thus set are suitably operated in association with the main nozzles to insert a plurality of weft yarns different in color.
In the above-described unit, theoretically a weft yarn can be selected freely. However, the practical use of the unit suffers from the following two problems: The first problem resides in the power of drive means, or motor. That is, in the conventional unit, the motor is rotated according to the quantity of yarn wound on the drum instead of the rotational condition of the loom body. Therefore, even in the case where two weft yarn storing units are alternately operated to jet two weft yarns different in color, the motors of the units repeatedly carry out an on-off operation in such a manner that as the quantity of yarn on the drum is decreased, the yarn is supplied for supplement. Therefore, the power consumption required for starting and stopping the motors is increased, and the amount of heat generated by the motors is also increased. If, in the case of alternately inserting two weft yarns different in color, the rpm of each motor is set to 1/2 of the rpm which is required when one weft yarn is inserted, then the above-described starting and stopping operations can be eliminated. In view of the foregoing, in order to decrease the frequency of on-off operations, a method has been employed in which the average weft insertion rate (weft insertion length per minute) of each weft yarn storing unit, and the rpm of the motor is manually adjusted according to the weft insertion rate. However, the method is disadvantageous in that the amounts of yarn wound on the drums change according to the jetting order, thus greatly increasing depending on the jetting order. Ideally, the quantity of yarn for only one weft insertion should be stored on the drum. However, if, in the case where the average value of the weft insertion rate is calculated and the rpm of the motor is set for the average weft insertion rate, the rpm of the motor is set to a half (1/2) of the rpm required for the continuous insertion of one yarn when the units are alternately operated to insert ten yarns each time, the unit which jets ten times earlier should store the quantity of yarn corresponding to five jetting operations, otherwise the quantity of yarn becomes short during operation. If, in order to eliminate this difficulty, an excessive amount of yarn is wound on the drum, then the yarns may tangle with each other, the yarn may be wound unsatisfactorily, and the unit itself is increased in size. As is apparent from the above description, the conventional unit suffers from the problem that fundamentally the power of the motor is not economically used. Solution of the problem would lower the reliability of the unit.
The second problem accompanying the conventional unit resides in the erroneous operation of the sensor 8. The sensor 8 is to determine whether or not the yarn is wound a predetermined number of turns on the drum. The sensor 8 is generally a reflection type photo-electric converter such as a photo-diode. Therefore, the sensor is liable to operate erroneously in the case where the yarn is thin or colored, for instance, in black; that is, in the case where it is optically difficult to detect the yarn. Furthermore, the erroneous operation may attribute to the mechanical reason that, for instance, the yarn is irregularly wound on the drum. The fact that the sensor essential for motor control is low in reliability is a serious drawback of the conventional unit. Accordingly, for stably storing the yarn, it is required to provide a weft yarn storing unit which needs no such stored-yarn-detecting sensor.